The present invention relates to circuits and methods for short circuit protection.
Many electronic products are made up of different integrated circuits (ICs) which are assembled to interface with each other and to other electronic devices. Some electronic assemblies may also be manufactured to interface with other assemblies. After final manufacturing is complete, these assemblies may make up a complete electronic product which may be used by an end user. A hard disk drive is an example of an assembly which may be installed or assembled inside another assembly such as a computer, for example.
These ICs and electronic assemblies may be handled during test and assembly of an intermediate or final product. The handling of these devices may cause inadvertent short circuits on the outputs of the integrated circuit or assembly. In a short circuit condition, an output of a device may be inadvertently connected to ground or a power supply terminal. This condition may cause increases in voltages or currents that may damage devices (e.g., transistors) in the IC. Short circuit conditions may be caused by a wide variety of manufacturing or end user factors.
FIG. 1 illustrates a short circuit condition in an amplifier circuit. Amplifier 100 is a class AB amplifier, which includes an input terminal 101 for receiving an input signal, a drive circuit for amplifying the input signal and generating drive signals to control the gate terminals of output transistors 103 and 104. PMOS transistor 103 has a gate (“pgate”) coupled to receive a drive signal, a source terminal coupled to a power supply Vdd, and a drain coupled to an output terminal 105 of the amplifier. PMOS transistor 103 receives the drive signal on “pgate” and generates an output current based on the voltage of the drive signal. Similarly, NMOS transistor 104 has a gate (“ngate”) coupled to receive a drive signal, a source terminal coupled to a ground, and a drain coupled to an output terminal 105 of the amplifier. NMOS transistor 103 receives the drive signal on “ngate” and generates an output current based on the voltage of the drive signal. In this example, the output terminal 105 of amplifier 100 is connected to drive one terminal of a differential load 106. The other terminal of load 106 is coupled to a second amplifier 107. A short circuit condition may occur if the output terminal 105 is inadvertently electrically connected (e.g., with zero resistance) to either the power supply terminal Vdd or ground. In either case, the voltages across the devices may be larger than the maximum allowable voltages, and the devices can be damaged or destroyed, resulting in a failure of the amplifier.
The present invention solves these and other problems by providing circuits and methods for short circuit protection.